Wire bonding method

ABSTRACT

A method and apparatus for wire bonding that allows easy checking and correction of bonding point coordinates in which upon the registration of the coordinates of fixed points used for alignment in a fixed point standard pattern storage memory and the subsequent registration of the coordinates of bonding points in a bonding point coordinate memory, the coordinates of bonding points and the images of pads or leads obtained by a camera at the time of the registration of the coordinates are both registered in an image data storage memory, so that the registered images are displayed on a monitor in cases where bonding point coordinates are checked or corrected at a later time.

This is a Divisional Application of application Ser. No. 08/735,994,filed Oct. 23, 1996, now U.S. Pat. No. 5,862,974.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wire bonding method and apparatus andmore particularly to a wire bonding method and apparatus which are usedwhen bonding point coordinates are registered and corrected.

2. Prior Art

FIG. 4 shows one of typical semiconductor devices. In this semiconductordevice, pellets 1 are mounted on lead frames 2, and pads 1 a 1 on thepellets 1 are connected to leads 2 a 1 on the lead frames 2 by means ofwires 3 a 1. FIG. 5 shows the designations of respective pads, leads andwires to which symbols indicating the bonding order have been assigned.In the following description, pads 1 a 1, 1 a 2 . . . 1 a 14 will bereferred to in general as 1 an, leads 2 a 1, 2 a 2 . . . 2 a 14 will bereferred to in general as 2 an, and wires 3 a 1, 3 a 2 . . . 3 a 14referred to in general as 3 an. In other words, pads 1 an and leads 2 anare connected by means of wires 3 an.

The wire bonding apparatus which connects the wires 3 an is constructedas shown in FIG. 6.

A bonding head 8 is mounted on an XY table 7 which is driven in the Xand Y directions by an X-axis motor 5 and a Y-axis motor 6. A bondingarm 9 is installed on this bonding head 8 so as to move upward anddownward or pivot. The bonding arm 9 is moved upward and downward orcaused to pivot by a Z-axis motor (not shown). A bonding tool 10 isfastened to the tip end of the bonding arm 9, and a wire (not shown) ispassed through this bonding tool 10. Furthermore, a camera holding part11 is fastened to the bonding head 8, and a camera 12 is attached to thetip end of the camera holding part 11 so as to be offset from thebonding tool 10. The workpieces 13 to which wires are connected are fedto the bonding position by a frame feeder 14.

In order to perform bonding using the wire bonding apparatus asdescribed above, it is necessary to register the bonding coordinatesbeforehand. In the registration of the bonding coordinates, a standardpattern which is used for workpiece alignment is first stored in memory,and positions which are used to store this pattern in memory areregistered as fixed points. Afterward, the registration of bondingcoordinates is performed. Generally, in semiconductor devices of thetype shown in FIG. 4, the relative positional relationship of therespective pads lan on the pellet 1 is fixed. Furthermore, the relativepositional relationship of the respective leads 2 an on the lead frame 2is also fixed. However, since the pellet 1 is fastened to the lead frame2 by adhesion, the positional relationship between the coordinates onthe side of the pellet 1 and the coordinates on the side of the leadframe 2 is usually different in each workpiece 13.

Generally, the bonding positions of the respective pads 1 an can becalculated by detecting the shift from the regular positions of at leasttwo fixed points on the pellet 1, and the bonding positions of therespective leads 2 is calculated by detecting the shift from the regularpositions of at least two fixed points on the lead frame 2. As a result,bonding is performed in the correct positions of the pads 1 an and leadframes 2 an. In more complicated semiconductor devices, there may be adetection of positional shifts that use a larger number of fixed points.

An example is described below in which two fixed points on the pelletside and two fixed points on the lead frame side are used. A method thatis generally used to perform such an alignment detection of fixed pointsincludes storing a standard pattern of fixed points in memory so thatregularizing correlation processing is performed. Naturally, however,other types of detection processing may also be used.

In particular, the registration of fixed points on the side of thepellet 1 is accomplished in the following manner:

Cruciform reticle marks which indicate the center of the camera 12 aredisplayed on the television monitor (called “monitor”) which shows theimages obtained by the camera 12; a chessman or digital switch whichdrives the XY table 7 is operated so that the XY table is moved and thecamera 12 is positioned above the pellet 1, and the chessman or digitalswitch is then operated (while the monitor is viewed by the operator) sothat the center of the reticle marks on the monitor is aligned with thedesired point. Then, a registration switch is pressed, thus causing thecoordinates of the XY table 7 to be registered in the bonding pointcoordinate memory as a first fixed point. At the same time, the standardpattern of this fixed point is registered in the fixed point standardpattern storage memory. By using a similar operation, a separate pointon the pellet 1 is registered as a second fixed point. Incidentally, twoseparated positions at opposite corners are selected as these fixedpoints. Fixed points on the side of the lead frame 2 are also registeredby means of a similar operation.

After the fixed points are registered, the bonding point coordinates arethen registered. As in the case described above, this registration ofbonding point coordinates is accomplished in the following manner:

The chessman or digital switch is operated so that the XY table 7 ismoved, thus causing the camera 12 to be positioned above the pad 1 an orlead 2 an that is to be bonded. Then, while viewing the monitor, theoperator operates the chessman or digital switch so that the center ofthe reticle marks on the monitor is aligned with the desired position ofthe pad 1 an or lead 2 an. Next, the registration switch is pressed sothat the coordinates of the XY table 7 are registered in the bondingpoint coordinate memory as bonding coordinates. This operation isperformed for all of the bonding points, so that the respective bondingpoint coordinates are registered in the bonding point coordinate memory.Generally, the desired bonding positions are set at the centers of thepads 1 an and leads 2 an.

By thus registering the coordinates of two fixed points on the side ofthe pellet 1, two fixed points on the side of the lead frame 2 and therespective bonding points, it is possible to detect any shift of thefixed points in subsequent workpieces 13 of the same type that are to bebonded. Accordingly, the bonding point coordinates can be automaticallycorrected so that wire bonding can be performed automatically. In otherwords, the camera 12 is moved to points above the regular fixed pointsthat have been registered beforehand so that any positional shift of theactual fixed points from the regular fixed points is detected. Then, theactual bonding point coordinates of the respective bonding points areautomatically calculated on the basis of these positional shiftdetection values, and the bonding tool 10 is guided to these correctedbonding points (i. e., the XY table 7 is moved to the respective bondingpoint coordinates), so that the bonding work is performed automatically.

Actual bonding work is accomplished by moving the XY table 7 tocoordinates obtained by adding the amount of offset between the centerof the camera 12 and the center of the bonding tool 10 to the respectivebonding point coordinates that have been corrected for the positionalshift, so that the bonding tool 10 is brought to the respective bondingpoints. The wire bonding methods and apparatuses of this type aredisclosed in, for instance, Japanese Patent Application Publication(Kokoku) Nos. 57-11498, 57-33852, 57-50059 and 61-6541.

Conventionally, in order to determine the positions of the bondingpoints after the coordinates of the fixed points and bonding points havebeen registered, the following method has been employed:

The XY table 7 is moved to the position of the stored bonding pointcoordinates, after which the pad 1 an or lead 2 an and the reticle marksshown on the monitor are examined, and a determination is made to see ifthere is any positional shift in the bonding point.

However, in cases where it is desired to check or correct bonding pointcoordinates after bonding has been completed or after the workpiece 13used for coordinate registration has been sent into a subsequentprocess, it is necessary to use a method in which the positions of thecoordinates are checked using a different workpiece 13 of the same type.

More specifically, in such a conventional method, the shift of the fixedpoints (i. e., at least two fixed points) from the positions of theregular bonding point coordinates is again detected, and the positionsof the actual bonding point coordinates of the respective bonding pointsare calculated on the basis of these detection values. Then, the XYtable 7 is moved to these corrected bonding point coordinate positions,and the pad 1 an or lead 2 an and reticle marks shown on the monitor ineach case are examined to see if there has been any positional shift inthe bonding point. Accordingly, the alignment of the two fixed pointsmust be performed accurately, and if there is any shift in thisalignment, the respective bonding points will appear to be shifted, sothat accurate checking or correction is impossible.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a wirebonding method and apparatus in which it is not necessary to resetanother workpiece when it is desired to check or correct bonding pointcoordinates, so that any shift that might arise from the accompanyingalignment operation required in the case of such resetting can beeliminated, thus allowing easy checking and correction of bonding pointpositions.

The object described above is accomplished by a unique method for a wirebonding method in which pads on pellets and leads on lead frames areconnected by wires, and the unique method of the present invention isthat when the coordinates of fixed points used for alignment andsubsequently the coordinates of bonding points are registered, thecoordinates of bonding points and the images of pads or leads, which areobtained by a camera at the time that the coordinates of bonding pointsare registered, are both registered, so that the registered images ofpads or leads are displayed on a television monitor when bonding pointcoordinates are subsequently checked or corrected.

The object is accomplished by a unique structure of the presentinvention for a wire bonding apparatus that includes:

a. a bonding tool which connects pads on pellets and leads on leadframes via wires,

b. a camera which takes images of the bonding surface,

c. an XY table which drives both the bonding tool and the camera in theX and Y directions,

d. a manual operating means which allows manual movement of the XYtable,

e. an image memory which stores the images obtained by the camera and atelevision monitor which displays the images,

f. an image operational control section which processes the imagesstored in the image memory and calculates the amount of shift in fixedpoints used for alignment,

g. a fixed point standard pattern storage memory which stores a standardpattern of fixed points,

h. a bonding point coordinate memory which stores the coordinates ofbonding points and fixed points, and

i. an apparatus operational control section which calculates the bondingpoint coordinates stored in the bonding point coordinate memory inaccordance with the positional shifts calculated by the imageoperational control section,

and the unique structure of the present invention is that the bondingapparatus further includes an image data storage memory which storesimage data supplied from the image memory, so that when the bondingpoint coordinates are registered in the bonding point coordinate memory,the image data (of the pads or leads) stored in the image memory at thetime of such a coordinate registration is also stored in the image datastorage memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram which illustrates one embodiment of thecontrol circuit part used in the wire bonding method and apparatus ofthe present invention;

FIG. 2 is a screen diagram which shows a specified pad with bondingpoint coordinates stored in the bonding point coordinate memory beingdisplayed on the television monitor;

FIG. 3 is a screen diagram which shows a plurality of pads beingdisplayed on the television monitor;

FIG. 4 is a plan view which illustrates one example of a semiconductorpart;

FIG. 5 is an explanatory diagram which shows the designations ofrespective pads, leads and wires to which symbols indicating the bondingorder have been assigned; and

FIG. 6 is a plan view which schematically illustrates the overallconstruction of a wire bonding apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the present invention will be described with referenceto FIGS. 1 through 6.

As shown in FIG. 1, the wire bonding apparatus of FIG. 6 mainly includesan image processing section 20 which processes images obtained by acamera 12, an apparatus driving section 30 which operates the wirebonding apparatus, and a manual operating means 40 which is used formanually operating the XY table 7.

The image processing section 20 includes: an image memory 22 whichstores image shapes inputted by the camera 12 via an image input means21, an image data storage memory 23 which stores image data from theimage memory 22, a fixed point standard pattern storage memory 24 whichstores fixed point standard patterns, an image control memory 25 inwhich image processing steps for the image memory 22 are stored, and animage operational controller 26 which processes images from the imagememory 22 in accordance with the procedures stored in the image controlmemory 25. Furthermore, images from the image memory 22 are displayed ona television monitor (called “monitor”) 27.

The apparatus driving section 30 includes: an X/Y-axis motor controller31, a bonding control memory 32 an apparatus operational controller 33,and a bonding point coordinate memory 34. The X/Y-axis motor controller31 controls an X-axis motor 5 and a Y-axis motor 6. The bonding controlmemory 32 stores control steps for controlling the X-axis motor 5 andY-axis motor 6 (for the purpose of bonding operations) and steps forcalculating the bonding point coordinates. The apparatus operationalcontroller 33 controls the X/Y-axis motor controller 31 and the bondingcontrol memory 32, and it also calculates the actual bonding pointcoordinates on the basis of positional shift amounts calculated by theimage operational control section 26 and bonding point coordinate datainputted by the manual operating means 40. The bonding point coordinatememory 34 stores the coordinates of fixed points and bonding pointsinputted by the manual operating means 40 or calculated by the apparatusoperational controller 33.

The manual operating means 40 includes a chessman 41, a digital switch42, a registration switch 43 and a call-up switch 44. The XY table 7 isoperated using either the chessman 41 or the digital switch 42.

Next, the registration method will be described. The registration of thefixed point coordinates and respective bonding point coordinates is thesame as that of the conventional method.

In the preferred embodiment, as described above, the image data storagememory 23 is provided in the bonding apparatus, and images of pads orleads at respective bonding point coordinates are arranged in the sameorder as the corresponding bonding point coordinates stored in thebonding point coordinate memory 34, and then such images are stored inthe image data storage memory 23. Furthermore, the bonding coordinatedata is expressed as data obtained by adding corrections (describedlater) to the XY table coordinate values actually measured at the timethe bonding coordinate registration is made.

More specifically, the coordinate data B (Bx, By) for the respectivebonding coordinates can be expressed by Equation 1 shown below, and inthis Equation 1,

Tx is the X coordinate value of the XY table at the time of bondingcoordinate registration,

Ty is the Y coordinate value of the XY table at the time of bondingcoordinate registration,

Dx is the X coordinate correction amount in cases where a correction isapplied to the coordinate position, and

Dy is the Y coordinate correction amount in cases where a correction isapplied to the coordinate position.

Tx, Ty, Dx and Dy are respectively stored in the bonding [point]coordinate memory 34.

Bx=Tx+Dx  Equation 1

By=Ty+Dy

The above registration method will be described in greater detail.First, registration of the fixed points is performed. This registrationis accomplished as follows:

First, the chessman 41 or digital switch 42 of the manual operatingmeans 40 is operated so that the XY table 7 is moved, thus causing thecamera 12 to be positioned above the first fixed point.

The first fixed point is imaged by the camera 12.

This image is converted into a digital signal by the image input means21, and is stored in the image memory 22.

The image shapes stored in this image memory 22 are processed by theimage operational controller 26 and displayed on the monitor 27.

Next, while viewing the monitor 27, the operator moves the XY table (byoperating the chessman 41 or digital switch 42) so that the center ofthe reticle marks on the monitor 27 is aligned with the first fixedpoint.

Then, the registration switch 43 is pressed. As a result, the imagestored in the image memory 22 at this point in time is stored(registered) in the fixed point standard pattern storage memory 24 bythe image operational control section 26; and the coordinates of the XYtable 7 are stored (registered) in the bonding point coordinate memory34 by the apparatus operational control section 33 as the first fixedpoint. In this case, the image and coordinates of the first fixed pointare registered at predetermined addresses in the fixed point standardpattern storage memory 24 and bonding point coordinate memory 34.

The second fixed point is also registered by means of a similaroperation.

Next, the registration of bonding point coordinates is performed. As inthe case, this registration of bonding point coordinates is accomplishedas follows:

The XY table 7 is moved by operating the chessman 41 or digital switch42, so that the camera 12 is positioned above the pad 1 an or lead 2 anthat is to be bonded. As a result, the pad 1 an or lead 2 an isdisplayed on the monitor 27.

Then, while viewing the monitor 27, the operator moves the XY table (byoperating the chessman 41 or digital switch 42) so that the center ofthe reticle marks on the monitor 27 is aligned with the desired positionof the pad 1 an or lead 2 an.

Next, the registration switch 43 is pressed.

When the coordinate data for the respective bonding points isregistered, the XY table coordinate values Tx and Ty actually measuredat the time of bonding coordinate registration are stored in memory, andthe storage in memory of the correction amounts Dx and Dy is cleared.

As a result, the image of the desired pad or lead stored in the imagememory 22 at this point is stored (registered) in the image data storagememory 23 by the image operational controller 26; and the coordinates ofthe XY table 7 are stored (registered) in the bonding point coordinatememory 34 by the apparatus operational controller 33 as bonding pointcoordinates. In this case, the bonding point image and coordinates arestored at addresses which are arranged in the same order in the imagedata storage memory 23 and bonding point coordinate memory 34. Thisoperation is performed for all of the bonding points, so that images andcoordinates for the respective bonding points are registered in theimage data storage memory 23 and bonding point coordinate memory 34.

Next, a case in which specified stored bonding point coordinates arechecked or corrected will be described.

In a case where a bonding point image and coordinates stored in theimage data storage memory 23 and bonding point coordinate memory 34 areto be called up, numbers arranged in the same order as the order ofregistration are inputted into the apparatus operational controller 33by pressing the call-up switch 44, whereupon the apparatus operationalcontroller 33 reads out the bonding point coordinates stored in thebonding point coordinate memory 34, also reads out the correspondingimage stored in the image data storage memory 23 via the imageoperational control section 26, and then displays this image on themonitor 27 through the image memory 22.

FIG. 2 illustrates a read-out image data for a pad 1 an that isdisplayed on the monitor 27. The position of the bonding pointcoordinates of the displayed image stored in the bonding pointcoordinate memory 34 is the center position C of the image. In caseswhere this is to be altered to a desired bonding point P, the chessman41 or digital switch 42 is operated so that the crossing point of thereticle marks 27 a is moved to the bonding point P. Then, when theregistration switch 43 is pressed, the amounts of movement Δx and Δyinvolved in the movement from point C to point P are converted intoamounts of movement of the XY table as shown by Equation 2, and Dx andDy are stored as correction amounts for the bonding point coordinatesstored in the bonding point coordinate memory 34. In Equation 2, k is acoefficient of conversion from image pixel values to XY table pulses.

Dx=k·Δx  Equation 2

Dy=k·Δy

In this case, if the image of the bonding point coordinates beingcorrected is subjected to enlargement processing when the image isdisplayed on the monitor 27, the image will be easier to see, so thatchecking of the coordinates is facilitated.

It is also possible to form a plurality of display windows, e. g., fourdisplay windows 27A, 27B, 27C and 27D as shown in FIG. 3, thusdisplaying bonding point coordinates for a plurality of pads stored inthe bonding point coordinate memory 34 on one screen. In such a case,since bonding point coordinates for a plurality of locations can bechecked on a single screen, the working efficiency is greatly improved.

The checking and correction of bonding point coordinates on the leadside can also be performed in a similar manner.

As seen from the above, since image shapes present in the image memory22 at the time that bonding point coordinates are registered in thebonding point coordinate memory 34 are registered in the image datastorage memory, images of bonding points that are to be checked orcorrected can be displayed on the monitor 27 at a later time whenchecking or correction of bonding point coordinates is subsequentlyperformed. Accordingly, there is no need to reset another workpiece, andcorrections can always be performed using the same coordinate system asthat used when the fixed point standard patterns were stored in memory.As a result, shifts arising from adjustment of the alignment can beeliminated, so that the checking and correction of desired bondingpoints can be performed easily and accurately.

As described in detail above, according to the present invention, whenthe registration of the coordinates of fixed points and the subsequentregistration of the coordinates of bonding points are performed, thecoordinates of bonding points and images of pads or leads obtained by acamera at the time of the registration of coordinates of bonding pointsare also registered, so that the registered images are displayed on atelevision monitor in cases where bonding point coordinates are checkedor corrected at a later time. Accordingly, in cases where it is desiredto check or correct bonding point coordinates, there is no need to resetanother workpiece, and the shift arising from adjustment of thealignment can be eliminated, so that the checking and correction ofbonding point positions can easily be accomplished.

What is claimed is:
 1. A wire bonding method comprising: (a) imaging abonding point with an imaging means; (b) displaying the image from theimaging means on a display means; (c) moving vertical marks on saiddisplay means to be centered on said bonding point to determinecoordinates of the bonding point; (d) registering the bonding point bystoring the image in an image data storage memory in a same order ascoordinates of the bonding point are stored in a bonding pointcoordinate memory; (e) repeating steps (a)-(d) for each bonding point;and (f) retrieving a registered image of a bonding point stored in theimage data storage memory and the associated bonding point coordinatesstored in the bonding point coordinate memory for more easily andaccurately checking and correcting the bonding point coordinates.